Among the actually available biocompatible materials, pyrolytic carbon seems to be one of the materials having the best biocompatible characteristics. Typically, the pyrolysis of carbon containing starting materials and depositing the so formed pyrolytic carbon on a substrate requires high temperatures in the range of from 800 to 1000.degree. C. and higher. Medical prosthetic devices for implantation of this kind and methods of manufacture are disclosed in U.S. Pat. Nos. 4,164,045, 3,952,334, 3,685,059 and 3,526,005. The common substrate materials, especially materials based on organic polymers, will be irreversibly impaired by such high temperatures. European Patent Specification EP 0 224 080 B1 and U.S. Pat. No. 5,370,684 disclose a method for manufacturing a prosthetic device, comprising a substrate made of an organic polymer ("DACRON", "TEFLON") and having a coating of biocompatible carbon material. The coating has been deposited on the substrate at relatively low temperatures by sputtering a carbon target at a given voltage and current. The thus obtained coating has a thickness of less than 1.0 micron. The thus obtained carbon material is said to consist of turbostratic carbon. The known method is complex and expensive and provides a relatively low productivity. In case of an improper contact, the extremely thin carbon layer may easily be stripped off from the substrate.
According to other proposals, for example British Patents 856,329 or 801,531, the characteristics of polymer substrates may be modified and/or improved by grafting a coating on the surface of the substrates. The grafted polymer layer may be obtained by means of radical graft polymerization starting from ethylenic unsaturated monomers. The radical graft polymerization reaction may be induced by ionizing radiation. A typical ethylenic unsaturated monomer is methyl acrylate. An extended list of other suited monomers includes vinylidene chloride. By means of the grafted coating, a number of different characteristics may be obtained or improved; however, the preparation of a coating comprising biocompatible characteristics is not stated.
Contrary thereof, there is still an existing demand for a relatively simple method for preparing in high productivity, a biocompatible material comprising a biocompatible carbon material which is chemically bound to a substrate.